System and method for motion capture in natural environments

Abstract

A system captures motion data in natural environments. A set of sources and a set of sensors are arranged on an object such as a human body. Each source emits ultrasonic signals detected by the sensors. A driver module is also arranged on the body. The driver module generates the ultrasonic signals for the set of sources and timing signals for the set of sensors. Distances between the set of sources and the set of sensors are measured based on a time of flight of the ultrasonic signals. Three dimensional locations of the set of sources and the set of sensors are determined from the distances. The distance measurements are refined using inertial components that provide rotation rates and accelerations. All these measurements together yield poses or configurations of the object.

1. A system for capturing motion data in natural environments, comprising:
 a set of sources arranged on an object capable of undergoing motion, in which each source is configured to emit ultrasonic signals; 
 a set of sensors arranged on the object, in which each sensor is configured to detect the ultrasonic signals; 
 a driver module arranged on the object, in which the driver module is configured to generate the ultrasonic signals for the set of sources and timing signals for the set of sensors, and in which the ultrasonic signals are synchronized to the timing signals; 
 means for measuring distances between the set of sources and the set of sensors based on a time of flight of the ultrasonic signals; 
 a set of inertial components arranged on the object; 
 means for determining 3D orientations of the set of inertial components; and 
 means for determining 3D locations of the set of sources and the set of sensors from the distances to capture motion data of the object, in which the 3D locations and the 3D orientations determine a six degree of freedom pose with respect to a world coordinate system, and wherein the six degree of freedom pose is determined using inverse kinematics processes. 
 
   
   
     2. The system of  claim 1 , in which the object is articulated. 
   
   
     3. The system of  claim 1 , in which the object is deformable. 
   
   
     4. The system of  claim 1 , in which the object is animate. 
   
   
     5. The system of  claim 1 , in which the object is inanimate. 
   
   
     6. The system of  claim 1 , in which a particular source and a particular sensor form a pair, which can move with respect to each other. 
   
   
     7. The system of  claim 1 , in which the 3D locations are with respect to a global coordinate system. 
   
   
     8. The system of  claim 1 , in which the set of inertial components include three-axis accelerometer, and a three-axis gyroscope. 
   
   
     9. The system of  claim 1 , in which the set of sources, the set of sensors and the set of inertial components are wearable by a user. 
   
   
     10. The system of  claim 1 , in which the set of sources, the set of sensors and the set of inertial components are connected to the means for determining the 3D locations and the means for determining the 3D orientations by a wireless link. 
   
   
     11. The system of  claim 1 , in which a frequency range of the ultrasonic signals is 40±2.5 kHz. 
   
   
     12. The system of  claim 1 , in which signals from the inertial components are low-pass filtered, and the ultrasonic signals are high-pass filtered and the low-pass and high-pass signals are carried on a signal wire before transmission to the means for determining 3D orientations of the set of inertial components. 
   
   
     13. The system of  claim 1 , in which the ultrasonic signals are time multiplexed pulses. 
   
   
     14. The system of  claim 1 , in which the pose is determined using an extended Kalman filter applied to the distances and orientations. 
   
   
     15. A method for capturing motion data in natural environments, comprising:
 arranging a set of sources on an object capable of undergoing motion, in which each source is configured to emit ultrasonic signals; 
 arranging a set of sensors on the object, in which each sensor is configured to detect the ultrasonic signals; 
 arranging a set of inertial components arranged on the object; 
 determining 3D orientations of the set of inertial components; 
 measuring distances between the set of sources and the set of sensors based on a time of flight of the ultrasonic signals; and 
 determining 3D locations of the set of sources and the set of sensors from the distances to capture motion data of the object, wherein the 3D locations and the 3D orientations determine a six degree of freedom pose with respect to a world coordinate system, and wherein the six degree of freedom pose is determined using inverse kinematics processes.